Centrifugal Pump Head
Centrifugal Pump Head
(OP)
Dear All,
More than a process engineering question, it could be considered a gardening problem.
How to determine the Centrifugal Pump Head for a given flowrate without using a Pressure Gauge? ( Characteristic Curves are not available )
Best regards,
Max
More than a process engineering question, it could be considered a gardening problem.
How to determine the Centrifugal Pump Head for a given flowrate without using a Pressure Gauge? ( Characteristic Curves are not available )
Best regards,
Max





RE: Centrifugal Pump Head
--Mike--
RE: Centrifugal Pump Head
There is the need of a further clarification: my question is how to evaluate a priori if the pump can do it ( given the flow-rate )?
Thanks
Max
RE: Centrifugal Pump Head
try connecting a gardenhose and hold up (1st or 2nd floor) the other end. when no more water comes out, the difference in height from the pump to the top of liquid in the hose is your shutoff head (in meters water kolom (0.9881 bar/m). than by timing the outflow (buckets per minute) at lower hieght, find the rest of your curve.
Have fun:)
RE: Centrifugal Pump Head
that should be 0.0979 bar/m water kolom
RE: Centrifugal Pump Head
Thanks,
Max
RE: Centrifugal Pump Head
Once water comes out the other end you can find the pump discharge pressure by:
P2 = P1 - dPf - dPh.
P2 = the pressure at the other end (1.014bara)
P1 = your pump discharge pressure (the point you actually want to fill in on your pump graph).
dPf = a bit more difficult. but can be approximated from dPf = 1/2 * rho * v^2 if v is low, like 0.5 m/s. So take a short lenght of the biggest hose you can find. Now measure flow by stopwastching your "buckets" (extrapolate to m3/h)and deviding that number by 0.25*pi*inside-hose-diameter^2 to find v. When your hose is long and thin, you'll have to use Reynolds, moody and frictionfactors (nasty bit of calculating which you realy want macros in excel to do for you).
RE: Centrifugal Pump Head
in a pump curve you set out flow against pump head.
now I come to think of it my previous answer can be done simpler if you can connect two hoses to the discharge end. read of waterkolemn height of one that is held to high for outflow (discharge pressure)and measure flow on the other one. Use a valve on the second hose to get more points on your pump curve. Now you are circumventing pressure loss from gardenhose.
RE: Centrifugal Pump Head
But if you know the pump impeller diameter and specific speed, you can generate a "generic" curve shape.
If you want to get more accurate than that you need to take the pump apart and study the number of impeller vanes and their outlet angle to get a better idea of the expected head coefficient.
RE: Centrifugal Pump Head
RE: Centrifugal Pump Head
@ bradshsi: Euler is fun, I'll give you that, but this involves a lot of guessing approach angles, front and back blade eddie loss, re circulation leakage loss, turbulence zone loss and assuming material friction factors and so on and so on.
My advice is this: If you want to know whats realy happening, get a T-piece, a tube, a valve, a bucket and a stopwatch.
@ max could you tell us a bit more about your problem?
RE: Centrifugal Pump Head
If you know the general construction of the pump you can make a decent stab at the curve shape. Lets take your list of items in turn:
Approach angles. Not really an issue in predicting a HQ curve unless the suction pipework is especially bad.
Front & back eddie loss. I presume you are referring to the expected vortex strength, which is reasonably predictable when the geometry is known.
Recirculation leakage loss. Again this can be predicted from the pump geometry. Note that leakage losses occur at all flow rates not just when the pump is operating in recirculation.
Turbulence zone loss. Not sure what you are referring to here. Most centrifugal pumps operate in the turbulent regime.
Friction factors. Provided the casting is not extremely rough or smooth these can be taken into account.
I'm not trying to be argumentative here. By far the easiest way to confirm the pump curve is by experimentation or a pressure gauge.
However if those are not an option, prediction from the geometry is a possibility.
RE: Centrifugal Pump Head
Supposing the following partial further information available:
Impeller Diameter: 200mm
Number of Vanes: 10
Approach Angle of Vanes:5%
Numero di stadi:1
Many Thanks,
Max
RE: Centrifugal Pump Head
RE: Centrifugal Pump Head
@Bradshsi: do you also have experience with experimental correlations for centrifugal air blowers? Ive got a problem with one and am thinking of starting a new thread if it's not to much to aks to share this kind of data. I'd certainly understand if youre reluctant to do so.
RE: Centrifugal Pump Head
No speed given, no driver size, no real data only very vague info lacking any real engineering input.
"it could be considered a gardening problem"
"Supposing the following partial further information available:"
RE: Centrifugal Pump Head
Thank you for the contributes;
the problem was a real gardening problem, however data are not available;
If you like, consider the following pump as reference:
Output: 1 HP,
Outlet: 2"
Rated: H 7.5 (M), Q 220 (L/M)
Maximum: H 12 (M), Q 450 (L/M)
Dimension: 350 L x 162 W x 180 H (mm)
Weight: 11 Kgs
Thanks again for the help, best regards
RE: Centrifugal Pump Head
That is assuming that chart is for your pump, and no motor or impellar changes have been made.
Am I missing something here?